At present, a number of signal amplification transistors are used in the radio frequency (RF) unit of a mobile communication base station, such as an eNB (evolved Node B) and RRH (Remote Radio Head). The kind of main transistor used in the radio frequency unit includes an LDMOS (Laterally Diffused Metal Oxide Semiconductor), GaN, GaAs, etc.
The stability of operation of these transistors is ensured in their operating voltage range, however, some transistors may become unstable during transition of power source when they are powered up. Because of this, if an amplification device satisfies a condition of oscillation when a transistor becomes unstable, for example, an instantaneous spurious is generated. Alternatively, the amplification device issues a device alarm etc. due to a rise in current during transition.
Some existing monolithic integrated circuits (IC) are designed to include a built-in power sequence control. This circuit design is intended to reduce the size of devices using IC chips by integrating the function of controlling power sequence into the chips themselves (for example, see Japanese Laid-open Patent Publication No. 06-140582).
As described above, some transistors may become unstable during transition of power source when they are powered up. Because of this, there has been such a problem that an amplification device may satisfy the condition of oscillation due to the unstable operation of the transistor.